Aqueous solutions of sodium phosphate salts (monobasic and dibasic sodium phosphate), such as FLEET® PHOSPHO-SODA®, are very effective oral cathartics and are extensively used prior to colonoscopy, radiographic procedures, and surgery. For pre-colonoscopy use, a split regimen is preferred that includes one 45 mL dose given the evening before colonoscopy and a second 45 mL dose given at least three hours prior to the procedure on the following morning. Each 45 mL dose contains 21.6 g monobasic sodium phosphate, and 8.1 g dibasic sodium phosphate. Patients are instructed to consume only a clear liquids diet for the meal proceeding the first dose, and to drink large amounts of clear liquids, including water and oral rehydration solutions, for example 3 to 4 liters, after each dose. See, for example, U.S. Published Patent Application publication no. US20040192614 to Vanner et al.